Hydrogen generating material, hydrogen generator and fuel cell

ABSTRACT

A hydrogen generating material reacts with water to produce hydrogen and includes at least one metal material selected from the group consisting of aluminum, magnesium, and their alloys. The metal material includes particles with a particle size of 60 μm or less in a proportion of 80 wt % or more. The hydrogen generating material can produce hydrogen easily and efficiently at low temperatures. A hydrogen generator can be made portable by using the hydrogen generating material. Moreover, the use of the hydrogen generating material as a hydrogen fuel source can reduce the size of a fuel cell and improve the electrical efficiency.

TECHNICAL FIELD

The present invention relates to a hydrogen generating materialincluding a metal material that reacts with water to produce hydrogen, ahydrogen generator using the hydrogen generating material, and a fuelcell using the hydrogen generating material as a hydrogen fuel source.

BACKGROUND ART

With the recent widespread use of cordless equipment such as a personalcomputer or portable telephone, secondary batteries used as a powersource of the cordless equipment are increasingly required to have asmaller size and higher capacity. At present, a lithium ion secondarybattery that can achieve a small size, light weight, and high energydensity is being put to practical use and growing in demand as aportable power source. However, depending on the type of cordlessequipment to be used, the lithium ion secondary battery is not yetreliable enough to ensure a continuous available time.

Under these circumstances, a polymer electrolyte fuel cell has beenstudied as an example of the battery that may meet the aboverequirements. The polymer electrolyte fuel cell uses a polymerelectrolyte membrane as an electrolyte, oxygen in the air as a positiveactive material, and a fuel (hydrogen, methanol, etc.) as a negativeactive material, and has attracted considerable attention because it isa battery system that can be expected to have a higher energy densitythan the lithium ion secondary battery. Fuel cells can be usedcontinuously as long as a fuel and oxygen are supplied. Although thereare several candidates for fuels used for the fuel cells, the individualfuels have various problems, and the final decision has not been madeyet.

A direct methanol fuel cell (DMFC) is miniaturized easily and expectedto be a future portable power source. In the DMFC, methanol is used as afuel and reacts directly at the electrode. However, the DMFC causes areduction in voltage due to a crossover phenomenon in which methanol atthe negative electrode passes through the solid electrolyte and reachesthe positive electrode. Therefore, the DMFC still does not have theexpected energy density.

When hydrogen is used as a fuel, e.g., a method for supplying hydrogenstored in a high-pressure tank or hydrogen-storing alloy tank isemployed to some extent. However, a fuel cell using such a tank is notsuitable for a portable power source, since both the volume and theweight of the fuel cell are increased, and the energy density isreduced. There is also another method for extracting hydrogen byreforming a hydrocarbon fuel. However, a fuel cell using the hydrocarbonfuel requires a reformer and thus poses problems such as the supply ofheat to the reformer and the thermal insulation. Therefore, this fuelcell is not suitable for a portable power source either.

Under these circumstances, a method has been proposed that produceshydrogen with a chemical reaction at a low temperature of 100° C. orless and uses the hydrogen as a fuel. For example, a metal that reactswith water to produce hydrogen such as aluminum, magnesium, silicon, orzinc is used as a hydrogen source (see the following Patent Documents 1to 5).

Patent Document 1: U.S. Pat. No. 6,506,360

Patent Document 2: JP 1(1989)-61301 A (U.S. Pat. No. 2,566,248)

Patent Document 3: JP 2004-231466 A

Patent Document 4: JP 2001-31401 A

Patent Document 5: JP 2004-505879 A

Patent Documents 1 to 3 disclose methods including the reaction ofaluminum and an alkali or acid. Although it may be easy for thesemethods to produce hydrogen chemically, the equivalent weight of thealkali or acid corresponding to aluminum needs to be added, which inturn reduces the energy density because of a large proportion of thematerial other than the hydrogen source. Moreover, the reaction product(oxide or hydroxide) forms a film on the surface of the metal, so thatwater cannot come into contact with the inside of the metal. This maylead to a problem that the oxidation reaction stops only at the surfaceof the metal. In particular, it is difficult for the method of PatentDocument 3, in which heat of the reaction between calcium oxide andwater is utilized in the hydrogen producing reaction of aluminum, togenerate hydrogen if the content of the calcium oxide is less than 15 wt%. In Patent Document 3, therefore, the proportion of aluminum in thehydrogen generating material is 85 wt % or less.

Patent Document 4 is intended to avoid the above problem by removing thefilm mechanically from the metal surface. However, the device shouldhave mechanical equipment for removal of the film and becomes larger. InPatent Document 5, alumina is added as a catalyst to suppress theformation of the hydroxide film, and hydrogen is generated at a lowtemperature of 50° C. However, the addition of a certain amount ofcatalyst can reduce the content of aluminum in the hydrogen generatingmaterial.

DISCLOSURE OF INVENTION

A hydrogen generating material of the present invention reacts withwater to produce hydrogen and includes at least one metal materialselected from the group consisting of aluminum, magnesium, and theiralloys. The metal material includes particles with a particle size of 60μm or less in a proportion of 80 wt % or more.

A hydrogen generator of the present invention includes a vessel havingat least an outlet through which hydrogen is discharged. The hydrogengenerating material of the present invention is placed in the vessel,and water is supplied to the hydrogen generating material to producehydrogen.

A fuel cell of the present invention includes the hydrogen generatingmaterial of the present invention as a hydrogen fuel source.

The hydrogen generating material of the present invention can producehydrogen easily and efficiently at low temperatures. A hydrogengenerator can be made portable by using the hydrogen generating materialof the present invention. Moreover, the use of the hydrogen generatingmaterial of the present invention as a hydrogen fuel source can reducethe size of a fuel cell and improve the electrical efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of ahydrogen generator of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a fuelcell of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail.

Embodiment 1

First, an embodiment of a hydrogen generating material of the presentinvention will be described. The hydrogen generating material of thepresent invention reacts with water to produce hydrogen and includes atleast one metal material selected from aluminum, magnesium, and theiralloys.

When the hydrogen generating material comes into contact with water, themetal material included in the hydrogen generating material and thewater can react to produce hydrogen.

The metal material generally forms a stable oxide film on the surface,and therefore the reaction with water hardly proceeds in the bulk statesuch as a plate or block. Even if the metal material is heated, it isunlikely to be a hydrogen gas source. However, the metal material in theform of fine particles can react with water to produce hydrogen, and thereaction accelerates particularly by heating. Thus, the metal materialin the form of fine particles can be used as an excellent hydrogensource. On the other hand, when the metal material does not react withwater, the handling of the metal material in the air is relatively easydue to the presence of the oxide film.

For example, when the metal material is aluminum, the reaction withwater to produce hydrogen and an oxidation product may be expressed asany one of the following formulas.2Al+6H₂O→Al₂O₃.3H₂O+3H₂  (1)2Al+4H₂O→Al₂O₃.H₂O+3H₂  (2)2Al+3H₂O→Al₂O₃+3H₂  (3)

In the above reaction, aluminum is stabilized by forming an oxide filmon the surface. However, since the reaction is an exothermic reaction,the reaction temperature is raised so that the reaction of aluminum andwater occurs readily, thus continuing the hydrogen producing reaction.In this case, if aluminum has an excessively large particle size, thereaction may not continue. Therefore, it is desirable that the particlesize of aluminum be as small as possible to increase the reaction area.The same is true for an aluminum alloy, magnesium, and a magnesiumalloy.

Although the compositions or the like of the aluminum alloy and themagnesium alloy are not particularly limited, it is desirable that thecontent of aluminum or magnesium that relates to the hydrogen generationbe larger. Specifically, the content of aluminum or magnesium ispreferably 80 wt % or more, and more preferably 85 wt % or more. Thatis, the content of the additional element is preferably 20 wt % or less,and more preferably 15 wt % or less. Depending on the type of theadditional element, the content is preferably 2 wt % or more so that theeffect of the additional element is exerted sufficiently.

Examples of the additional element in the aluminum alloy includesilicon, iron, copper, manganese, magnesium, zinc, nickel, titanium,lead, tin, and chromium. These elements may be used in combination oftwo or more. Among them, silicon, magnesium, and copper are preferredparticularly. The contents of silicon, magnesium, and copper may be 4 to13 wt %, 2 to 10 wt %, and 3 to 6 wt %, respectively. However, when twoor more of these elements are added, it is recommended that the totalamount of the additional elements including at least two elementsselected from silicon, magnesium, and copper should be adjusted tosatisfy the appropriate value of 20 wt % or less. The aluminum alloywith this composition can have hardness (e.g., 55 to 95 HB in Brinellhardness) that is higher than pure aluminum and is suitable fortreatment to remove the oxide film from the surface, as will bedescribed later. Moreover, the aluminum alloy can improve the reactivitywith water, and thus is expected to increase the amount of hydrogengenerated.

Examples of the additional element in the magnesium alloy includealuminum, zinc, zirconium, silicon, iron, copper, manganese, nickel, anda rare-earth element. These elements may be used in combination of twoor more. In particular, the magnesium alloy preferably includes at leastone element selected from aluminum, zinc, and zirconium. The preferredrange of the content depends on the type of the additional element, andaluminum, zinc, and zirconium may be 4 to 12 wt %, 1 to 8 wt %, and 0.2to 4 wt %, respectively. However, when two or more of these elements areadded, it is recommended that the total amount of the additionalelements including at least two elements selected from aluminum, zinc,and zirconium should be adjusted to satisfy the appropriate value of 20wt % or less. Like the aluminum alloy, the magnesium alloy with thiscomposition can be harder (e.g., 55 to 95 HB in Brinell hardness), andalso is expected to increase the amount of hydrogen generated.

There is no particular limitation to the manufacturing method or shapeof the metal material. The metal material may be produced, e.g., by amechanical powdering or atomizing method in a variety of shapes such asscale, substantially sphere, fusiform, and droplet. In particular, themetal material produced by a rapid solidification process like theatomizing method is used preferably. With the rapid solidificationprocess, crystal grains in the metal material become finer, and thegrain boundary that is to be an active site is increased. Therefore, thereaction of the metal material and water may proceed easily. Moreover,the metal material produced by the rapid solidification process hasrelatively high wettability and may be likely to react with water.

In the atomizing method, molten metal is fed as a narrow flow, and ashearing force is applied to the molten metal flow with an atomizerusing a gas or spinning disk, so that the molten metal flow is dispersedin the form of powder. A dispersion medium for the gas may be air orinert gas such as nitrogen or argon. When solution particles dispersedin the dispersion medium are cooled rapidly by spraying a liquid or gas,the solution particles are coagulated to form metal powder. The liquidor gas used as a cooling medium may be, e.g., water, liquid nitrogen,air, nitrogen, or argon.

When the metal material is produced by the mechanical powdering method,a lubricant is used in a dry process. The lubricant covers the surfaceof the metal material and reduces the wettability of the metal materialwith water. Therefore, even if the metal material is in the form of fineparticles, the reaction may not proceed easily. In such a case, thewettability can be enhanced by surface treatment, which will bedescribed later.

The form of the metal material used in the present inventionspecifically is as follows. In order for the metal material to reactwith water efficiently at low temperatures, the particle size ispreferably 100 μm or less, and more preferably 50 μm or less. Inparticular, for the purpose of producing hydrogen under the mildconditions of about 40° C., the optimum metal material includesparticles with a particle size of 60 μm or less in a proportion of 80 wt% or more, preferably 90 wt % or more, and further preferably 100 wt %.

To improve the reaction efficiency further, the average particle size ofthe metal material is preferably 30 μm or less, and more preferably 20μm or less.

The hydrogen generation rate increases as the particle size of the metalmaterial decreases. However, if the particle size is smaller than 0.1μm, it is difficult to handle the particles because their stability inthe air is lower. Moreover, the bulk density is reduced to reduce thepacking density of the hydrogen generating material. Therefore, it isdesirable that the particle size of the metal material be 0.1 μm ormore.

In this specification, the particle size of the metal material ismeasured, in principle, by a laser diffraction scattering method.Specifically, the measuring object is dispersed in a liquid phase suchas water and irradiated with a laser beam to detect scattering intensitydistribution, and the particle size distribution is measured using thisscattering intensity distribution. The measuring device may be, e.g.,“Microtrac HRA” (particle size analyzer, manufactured by Nikkiso Co.,Ltd.). For more convenience, the metal material having a desiredparticle size can be obtained by classification with a sieve. Forexample, when the metal material is classified with a 50 μm mesh sieve,the resultant powder has a particle size of 50 μm or less. In thisspecification, the average particle size means a diameter of particleswith an accumulated volume percentage of 50%, i.e., d₅₀.

It is desirable that the hydrogen generating material include a heatgenerating material that generates heat by reacting with water at roomtemperature along with the metal material so that the metal material iswarmed at 40° C. or more. In this specification, the room temperature is25° C. As described above, the metal material having a small particlesize is likely to be mixed uniformly with the heat generating material,and thus more favorable result may be obtained.

It is desirable that the metal material and the heat generating materialbe mixed so that only the metal material is not formed into a lump of 1mm or more. This can avoid interfering with the reaction between themetal material and water.

When the metal material with the above particle size and the heatgenerating material are mixed uniformly, the whole metal material isheated and reacts efficiently with water to produce hydrogen. Therefore,the metal material that serves as a hydrogen source can be increasedwhile reducing the proportion of the heat generating material in thehydrogen generating material. On the other hand, if the metal materialis in the form of fine particles and mixed with a large proportion ofthe heat generating material, the reaction proceeds very rapidly andheat is generated vigorously. Thus, there is a risk that the hydrogenproducing reaction may not be controlled. In view of this, theproportion of the heat generating material to the whole hydrogengenerating material is preferably not more than 20 wt %, and morepreferably less than 15 wt %.

If the hydrogen generating material includes no heat generatingmaterial, the hydrogen producing reaction does not start or takes aconsiderable time to start at low temperatures near the roomtemperature. Therefore, it is desirable that at least 1 wt % heatgenerating material be included in the hydrogen generating material.When the hydrogen generating material does not include the heatgenerating material, it may be heated externally to promote thereaction.

In the hydrogen generating material of the present invention, theproportion of the metal material to the total weight of the metalmaterial and the heat generating material is preferably more than 85 wt% and not more than 99 wt %. This can produce a larger amount ofhydrogen.

The reaction temperature and the hydrogen generation rate may becontrolled to some extent by the content of the heat generatingmaterial. However, if the reaction temperature is too high, the hydrogenproducing reaction proceeds rapidly and cannot be controlled. Therefore,it is desirable to adjust the amount of the heat generating materialadded so that the reaction temperature is 120° C. or less. Moreover, toprevent evaporation of water to be used for the reaction, it is moredesirable to adjust the amount of the heat generating material added sothat the reaction temperature is 100° C. or less. In terms of efficiencyof the hydrogen producing reaction, the reaction temperature ispreferably 40° C. or more.

The heat generating material that generates heat by reacting with watermay be, e.g., an oxide, a chloride, a sulfide, etc. of alkali metals oralkaline-earth metals that react with water to form a hydroxide orgenerate heat by hydration, such as calcium oxide, magnesium oxide,calcium chloride, magnesium chloride, or calcium sulfate. In particular,calcium oxide is most preferred because it is inexpensive and the amountof heat generated per unit weight is large.

A material that generates heat by reacting with oxygen such as ironpowder also has been known as the heat generating material. For thistype of heat generating material, however, oxygen needs to be introducedduring the reaction. Therefore, when the metal material and the heatgenerating material are placed in the same reactor, as in the case of ahydrogen generator of the present invention (which will be describedlater), the following problem is likely to occur: the purity of hydrogengenerated is reduced, or the amount of hydrogen generated is reduced dueto oxidation of the metal material that serves as a hydrogen source.Thus, the above material that generates heat by reacting with water isused suitably for the heat generating material of the present invention.

The metal material and the heat generating material are mixed and usedas the hydrogen generating material. Alternatively, the hydrogengenerating material can be a composite material obtained by coating thesurface of the metal material with the heat generating material.

Although the metal material may be used as it is, the metal materialpreferably is subjected to surface treatment before mixing with the heatgenerating material, thereby increasing the hydrogen generation rate.The surface treatment improves the surface reactivity of the metalmaterial by removing a film (e.g., oxide film) that may interfere withthe reaction from the surface of the metal material, or corroding thesurface of the metal material to enhance the hydrophilicity. A specificmeans for the surface treatment is not particularly limited. Forexample, there is a mechanical means for stirring the metal materialmechanically in an inert gas atmosphere, or in an organic solvent suchas toluene, ethanol, or acetone, or a solvent such as water. There isalso a chemical means for dissolving the surface of the metal materialwith an alkaline aqueous solution. Examples of the alkaline aqueoussolution include aqueous solutions of sodium hydroxide, potassiumhydroxide, and ammonia. The alkaline aqueous solution may have a pH ofabout 9 to 14. It is desirable that the surface-treated metal materialbe mixed with the heat generating material in the inert gas atmosphereso as to prevent the surface from being oxidized again.

The shape of the hydrogen generating material of the present inventionis not particularly limited. For example, the hydrogen generatingmaterial may be press-formed into pellets or granulated into granules toincrease the packing density.

A reaction accelerator such as alumina, silica, magnesia, zinc oxide,carbon, or water-absorbing polymer may be added to the hydrogengenerating material of the present invention. The addition of thereaction accelerator is considered to have the effect of making goodcontact between the metal material and water or facilitating thepenetration of water into pellets when the hydrogen generating materialis in the form of pellets.

Embodiment 2

Next, an embodiment of a hydrogen generator of the present inventionwill be described. The hydrogen generator of the present inventionincludes a vessel having at least an outlet through which hydrogenflows. The hydrogen generating material of Embodiment 1 is placed in thevessel, and water is supplied to the hydrogen generating material toproduce hydrogen.

By using the hydrogen generating material of Embodiment 1, hydrogen canbe produced easily and efficiently at low temperatures, and the hydrogengenerator can be made portable.

The hydrogen generating material reacts with water in the vessel and canproduce hydrogen that serves as a fuel source of a fuel cell, which willbe described later. In this case, the amount of hydrogen generated canbe controlled by controlling the supply of water to the hydrogengenerating material.

The material or shape of the vessel is not particularly limited, as longas the vessel can hold the hydrogen generating material. The suitablematerial for the vessel is substantially impermeable to water andhydrogen and does not cause any failure of the vessel even if it isheated at about 100° C. For example, metals such as aluminum and iron,resins such as polyethylene and polypropylene, or heat-resistant glasscan be used appropriately. Moreover, a means for supplying water to thevessel is not particularly limited. When water is supplied from outsidethe vessel, a water inlet may be provided in the vessel and connected toa pump or the like, thereby allowing water to flow into the vessel.

The vessel containing the hydrogen generating material, i.e., thehydrogen generator may be formed as a cartridge that is detachable fromthe main body of electronic equipment or the fuel cell body. In such acase, for the convenience of portability, the vessel may have a storageportion for storing water inside the vessel, and water may be suppliedfrom the storage portion to the hydrogen generating material. Thisconfiguration can remove the water inlet and the pump or the like, sothat the hydrogen generator can be configured simply by providing thevessel with at least a hydrogen outlet. Therefore, compared to thedevice in which water is supplied from outside the vessel, the hydrogengenerator can be simplified and miniaturized easily, and thus is moresuitable for a portable fuel source. The storage portion may be formed,e.g., by sealing water in a bag made of a polyethylene film or the like.The water inside the bag is brought into contact with the hydrogengenerating material in such a simple manner that the bag is perforated.Consequently, hydrogen can be produced in the vessel that functions as ahydrogen generator.

The hydrogen generator of the present invention will be described withreference to the drawing. FIG. 1 is a schematic cross-sectional viewshowing an example of the hydrogen generator of the present invention.In FIG. 1, the hydrogen generator 1 includes a vessel 2 and a lid 3, andthe lid 3 has an inlet 4 through which water is supplied and an outlet 5through which hydrogen is discharged. The inlet 4 and a tubular pump 6are connected by a supply pipe 7. A discharge pipe 8 is connected to theoutlet 5. The hydrogen generating material 9 of Embodiment 1 is placedin the vessel 2. While water 10 is supplied continuously to the hydrogengenerator 1 with the tubular pump 6, the hydrogen generating material 9and the water 10 react to produce hydrogen. This hydrogen (H₂) is drawnfrom the discharge pipe 8 connected to the outlet 5 and can be used as ahydrogen source of a fuel cell, which will be described later.

Embodiment 3

Next, an embodiment of a fuel cell of the present invention will bedescribed. The fuel cell of the present invention includes the hydrogengenerating material of Embodiment 1 as a hydrogen fuel source. This canreduce the size of the fuel cell and improve the electrical efficiency.

Hydrogen generated by the reaction of the hydrogen generating materialof Embodiment 1 includes neither CO nor CO₂, which have been a problemof hydrogen produced by reforming a hydrocarbon fuel. Therefore, even ifthe hydrogen is applied to a polymer electrolyte fuel cell that operatesat 100° C. or less, the fuel cell is not affected by poisoning due tothe above gas. Moreover, since the hydrogen producing reaction involveswater, the hydrogen gas generated includes a moderate amount of moistureand is very useful for the hydrogen source of the fuel cell that useshydrogen as a fuel.

The fuel cell of the present invention may receive hydrogen from thehydrogen generator of Embodiment 2. This can make the fuel cellportable.

The fuel cell of the present invention will be described with referenceto the drawing. FIG. 2 is a schematic cross-sectional view showing anexample of the fuel cell of the present invention. The fuel cell 20includes a membrane electrode assembly that includes a positiveelectrode 22 for reducing oxygen, a negative electrode 21 for oxidizinghydrogen, and a solid electrolyte 23 located between the positiveelectrode 22 and the negative electrode 21. The fuel cell 20 can operatecontinuously, e.g., by supplying hydrogen from the hydrogen generator(not shown in FIG. 2) of Embodiment 2.

A diffusion layer 24 is arranged on the outside of each of the positiveelectrode 22 and the negative electrode 21. The diffusion layer 24 maybe, e.g., a porous carbon material. A positive separator 26 is locatedon the side of the positive electrode 22 for supplying air (oxygen). Anegative separator 25 is located on the side of the negative electrode21 for supplying hydrogen. The negative separator 25 communicates with,e.g., the hydrogen generator (not shown in FIG. 2) of Embodiment 2. Thepositive electrode 22 has a positive terminal 28, and the negativeelectrode 21 has a negative terminal 27.

The fuel cell 20 is not limited particularly by its size, shape, ormaterial other than the hydrogen generator of Embodiment 2 and thehydrogen generating material of Embodiment 1 used in the hydrogengenerator.

Hereinafter, the present invention will be described by way of examples.

Working Example 1

Aluminum powder (the proportion of particles with a particle size of 60μm or less: 100 wt %) having an average particle size of 3 μm wasproduced by a gas atomizing method and used as a metal material. Calciumoxide powder was used as a heat generating material. The aluminum powderand the calcium oxide powder were mixed in a mortar at a ratio as shownin Table 1, thereby producing a hydrogen generating material. Then, 1 gof the hydrogen generating material was put in a sampling bottle, towhich 4 g of water was added and allowed to stand for 48 hours. Hydrogengenerated during this period of time was collected by awater-displacement method. The test was conducted at the temperature ofa room (24 to 26° C.), and the volume of the collected hydrogen wasmeasured as the amount of hydrogen generated. Table 1 shows the results.The maximum reaction temperature of the hydrogen generating materialincluding 1 wt % heat generating material was 89° C. during the test.

TABLE 1 Metal material Content (wt %) Average Heat Heat Amount ofparticle gener- Metal gener- hydrogen size ating mate- ating generatedType (μm) material rial material (mL) Working Alumi- 3 Calcium 99 1 886Example 1 num oxide 97 3 930 95 5 922 90 10 948 85 15 827 80 20 517 7030 439

Working Example 2

A hydrogen generating material was produced in the same manner asWorking Example 1 except that aluminum powder (the proportion ofparticles with a particle size of 60 μm or less: 100 wt %) having anaverage particle size of 30 μm was mixed at a ratio as shown in Table 2,instead of the aluminum powder having an average particle size of 3 μm.Subsequently, the amount of hydrogen generated was measured in the samemanner as Working Example 1. Table 2 shows the results.

Working Example 3

A hydrogen generating material was produced in the same manner asWorking Example 2 except that calcium chloride powder was mixed at aratio as shown in Table 2, instead of the calcium oxide powder.Subsequently, the amount of hydrogen generated was measured in the samemanner as Working Example 1. Table 2 shows the result.

Working Example 4

A hydrogen generating material was produced in the same manner asWorking Example 1 except that magnesium powder with a particle size of45 μm or less obtained by sieving was mixed at a ratio as shown in Table2, instead of the aluminum powder having an average particle size of 3μm. Subsequently, the amount of hydrogen generated was measured in thesame manner as Working Example 1. Table 2 shows the result.

Comparative Example 1

A hydrogen generating material was produced in the same manner asWorking Example 1 except that aluminum powder (the proportion ofparticles with a particle size of 60 μm or less: 16 wt %) having anaverage particle size of 150 μm was mixed at a ratio as shown in Table2, instead of the aluminum powder having an average particle size of 3μm. Subsequently, the amount of hydrogen generated was measured in thesame manner as Working Example 1. Table 2 shows the result.

Comparative Example 2

A hydrogen generating material was produced in the same manner asWorking Example 1 except that magnesium powder (the proportion ofparticles with a particle size of 60 μm or less: 12 wt %) having anaverage particle size of 150 μm was mixed at a ratio as shown in Table2, instead of the aluminum powder having an average particle size of 3μm. Subsequently, the amount of hydrogen generated was measured in thesame manner as Working Example 1. Table 2 shows the result.

Comparative Example 3

A hydrogen generating material was produced in the same manner asWorking Example 1 except that silicon powder having an average particlesize of 5 μm was mixed at a ratio as shown in Table 2, instead of thealuminum powder having an average particle size of 3 μm. Subsequently,the amount of hydrogen generated was measured in the same manner asWorking Example 1. Table 2 shows the result.

Comparative Example 4

A hydrogen generating material was produced in the same manner asWorking Example 1 except that zinc powder having an average particlesize of 7 μm was mixed at a ratio as shown in Table 2, instead of thealuminum powder having an average particle size of 3 μm. Subsequently,the amount of hydrogen generated was measured in the same manner asWorking Example 1. Table 2 shows the result.

TABLE 2 Metal material Content (wt %) Average Heat Heat Amount ofparticle gener- Metal gener- hydrogen size ating mate- ating generatedType (μm) material rial material (mL) Working Alumi- 30 Calcium 95 5 576Example num oxide 85 15 681 2 80 20 305 70 30 280 Working Alumi- 30Calcium 95 5 452 Example 3 num chloride Working Magne- ≦45 Calcium 95 5152 Example 4 sium oxide Compar- Alumi- 150 Calcium 95 5 321 ative numoxide Example 1 Compar- Magne- 150 3 ative sium Example 2 Compar-Silicon 5 86 ative Example 3 Compar- Zinc 7 72 ative Example 4

In Working Examples 1 to 4, the particle size of the metal material inthe hydrogen generating material is reduced, and the proportion of theparticles with a particle size of 60 μm or less is 80 wt % or more. Whencomparisons are made between the hydrogen generating materials includingthe same metal material, the amount of hydrogen generated is larger inWorking Examples 1 to 4 than in Comparative Example 1 or 2 that uses themetal material having a large particle size. Accordingly, the hydrogengenerating materials of Working Examples 1 to 4 can improve the reactionefficiency. Therefore, even if the proportion of the heat generatingmaterial is decreased to less than 15 wt %, the reaction of the metalmaterial and water can be continued. This makes it clear that thereaction efficiency is improved as the proportion of the heat generatingmaterial becomes lower.

In particular, Working Example 1 in which the metal material has anaverage particle size of 3 μm can produce a hydrogen gas correspondingto about 70% of the theoretical value (Al: about 1.3 L per 1 g) of thehydrogen generation, although the proportion of the heat generatingmaterial is as low as 1 wt %. Moreover, even under the mild conditionsof 100° C. or less, the hydrogen producing reaction can proceedefficiently.

In both Comparative Example 3 using silicon as the metal material andComparative Example 4 using zinc as the metal material, the amount ofhydrogen generated is small, although the metal material includes fineparticles having an average particle size of 10 μm or less. This makesit clear that aluminum or magnesium is more suitable than the others forthe metal material that serves as a hydrogen source.

The hydrogen generating material of Comparative Example 1 can produce ahydrogen gas to some extent, although the aluminum powder includes only16 wt % particles with a particle size of 60 μm or less. This isattributed to an increase in reactivity with water because the aluminumpowder is formed by the gas atomizing method.

Working Example 5

A hydrogen generating material was produced in the same manner asWorking Example 1 except that the aluminum powder and the calcium oxidepowder were mixed at a ratio as shown in Table 3. Then, 1 g of thehydrogen generating material was press-formed at a pressure of 40 MPainto pellets having a diameter of 12 mm. Using these pellets, the amountof hydrogen generated was measured in the same manner as WorkingExample 1. Table 3 shows the result.

Working Example 6

A hydrogen generating material was produced in the same manner asWorking Example 1 except that the aluminum powder, the calcium oxidepowder, and alumina having an average particle size of 1 μm were mixedat a ratio as shown in Table 3. Then, the hydrogen generating materialwas formed into pellets in the same manner as Working Example 5. Usingthese pellets, the amount of hydrogen generated was measured in the samemanner as Working Example 1. Table 3 shows the result.

TABLE 3 Shape of Amount of Content (wt %) hydrogen hydrogen Calciumgenerating generated Aluminum oxide Alumina material (mL) Working 85 15— Pellet 190 Example 5 Working 81 14 5 Pellet 276 Example 6

The results of Working Examples 5, 6 confirmed that the hydrogengenerating material of the present invention brings about a hydrogenproducing reaction even in the form of pellets. It was also confirmedthat the addition of alumina improves the reaction efficiency.

Working Example 7

1 g of the hydrogen generating material including only aluminum powderused in Working Example 1 and 2 g of water were put in a samplingbottle. A heating resistor was located outside the sampling bottle. Thesampling bottle was heated at various temperatures by allowingelectricity to pass through the resistor, so that the hydrogengenerating material reacted with water. Hydrogen thus generated wascollected by water substitution. The amount of hydrogen generated andthe generation rate were measured over 20 hours from the beginning ofthe experiment. Table 4 shows the amount of hydrogen generated (totalamount) and the maximum generation rate during this period of time. InTable 4, “non-heating” indicates that the measurement was performed atthe temperature of a room (24 to 26° C.) while no electricity passedthough the resistor.

TABLE 4 Amount of Maximum Heating hydrogen generation temperaturegenerated rate (° C.) (mL) (mL/min) Working non-heating 0 0 Example 7 3024 <1 40 968 3 45 974 9 50 1061 19

In Working Example 7, when heating stopped and the hydrogen generatingmaterial and water were cooled, the hydrogen generation stopped afterseveral minutes. Moreover, no hydrogen was generated without heating.

Working Example 8

The amount of hydrogen generated and the generation rate were measuredin the same manner as Working Example 7 except that aluminum powderhaving various average particle sizes as shown in Table 5 was used, 10 gof water was added, and the heating temperature was 50° C. Table 5 showsthe results.

Comparative Example 5

The amount of hydrogen generated and the generation rate were measuredin the same manner as Working Example 8 except that the aluminum powderof Comparative Example 1 was used instead of the aluminum powder ofWorking Example 1. Table 5 shows the result.

Comparative Example 6

The amount of hydrogen generated and the generation rate were measuredin the same manner as Working Example 8 except that aluminum powder (theproportion of particles with a particle size of 60 μm or less: 70 wt %)having an average particle size of 55 μm was used instead of thealuminum powder of Working Example 1. Table 5 shows the result.

Working Example 9

The aluminum powder having an average particle size of 55 μm used inComparative Example 6 was screened with a 250-mesh sieve. The aluminumpowder that passed through the sieve included 87 wt % particles with aparticle size of 60 μm or less. The amount of hydrogen generated and thegeneration rate were measured in the same manner as Working Example 8except that the aluminum powder that passed through the sieve was usedinstead of the aluminum powder of Working Example 1. Table 5 shows theresult.

TABLE 5 Proportion of Maximum Heating Average particles Amount of gener-temper- particle of 60 μm hydrogen ation ature size or less generatedrate (° C.) (μm) (wt %) (mL) (mL/min) Working 50 3 100 1027 12 Example20 100 921 5 8 30 100 631 3 Working 50 <55 87 535 2 Example 9 Compar- 50150 16 365 1 ative Example 5 Compar- 50 55 70 375 2 ative Example 6

As shown in Table 4, the metal material included in the hydrogengenerating material of the present invention is not likely to react withwater at 30° C. or less. Therefore, when the hydrogen generatingmaterial does not include a heat generating material, it is desirablethat the reaction start with external heating or the like. In such acase, since the reaction proceeds under the mild conditions of about 40°C., heating at a temperature of at least 40° C. can provide sufficientreaction efficiency. Therefore, the hydrogen generating material canproduce hydrogen even with a simple heating facility, and thus issuitable for a hydrogen source of a small fuel cell that requires asmall compact fuel source.

As is evident from the results of Table 5, even if the heat generatingmaterial is not present, the hydrogen producing reaction can be likelyto occur by using only small particles obtained by screening as themetal material. In particular, when the average particle size is 20 μmor less, the reaction efficiency can be improved significantly.

Working Example 10

An aluminum alloy “ADC6” (composition: Al content: 97 wt %, Mg content:2.5 wt %, form: cutting chips, Brinell hardness: 67 HB) based on theJapan Industrial Standard (JIS) was subjected to surface treatment thatremoves the oxide film from the surface while mechanically stirring thealuminum alloy in water, thus resulting in aluminum alloy powder (theproportion of particles with a particle size of 60 μm or less: 100 wt %)having an average particle size of 10 μm. This metal material andcalcium oxide were mixed in a mortar at a ratio as shown in Table 6,thereby producing a hydrogen generating material. The amount of hydrogengenerated was measured in the same manner as Working Example 1 exceptfor the use of the above hydrogen generating material. Table 6 shows theresults. The maximum reaction temperature of the hydrogen generatingmaterial including 1 wt % heat generating material was 87° C. during thetest.

Working Example 11

A hydrogen generating material was produced in the same manner asWorking Example 10 except that the aluminum alloy powder having anaverage particle size of 50 μm (the proportion of particles with aparticle size of 60 μm or less: 82 wt %) was mixed with calcium oxide ata ratio as shown in Table 6. Subsequently, the amount of hydrogengenerated was measured in the same manner as Working Example 1. Table 6shows the results.

Working Example 12

Instead of the aluminum alloy “ADC6”, the following aluminum alloysbased on the JIS were used: “ADC3” (composition: Al content: 88 wt %, Sicontent: 10 wt %, Mg content: 0.5 wt %, form: cutting chip, Brinellhardness: 76 HB); “ADC1” (composition: Al content: 85 wt %, Si content:12 wt %, form: cutting chips, Brinell hardness: 72 HB); and “AC4B”(composition: Al content: 80 wt %, Si content: 10 wt %, Cu content: 4 wt%, form: cutting chips, Brinell hardness: 80 HB). Three types ofhydrogen generating materials were produced in the same manner asWorking Example 11 except that each of the above metal materials wasmixed with calcium oxide at a ratio as shown in Table 6. Subsequently,the amount of hydrogen generated was measured in the same manner asWorking Example 1. Table 6 shows the results.

TABLE 6 Metal material Average Content (wt %) Amount of Mate- particleAl Metal hydrogen rial size content mate- Calcium generated (JIS) (μm)(wt %) rial oxide (mL) Working ADC6 10 97 99 1 899 Example 10 97 3 94495 5 935 90 10 962 86 14 837 80 20 520 70 30 454 Working ADC6 50 97 95 5654 Example 11 86 14 700 80 20 327 70 30 301 Working ADC3 50 88 95 5 610Example 12 ADC1 85 603 AC4B 80 579

Working Example 13

A hydrogen generating material was produced in the same manner asWorking Example 10 except that a magnesium alloy “MC10” (composition: Mgcontent: 94 wt %, Zn content: 4 wt %, Zr content: 0.8 wt %, form:cutting chips) based on the JIS was used instead of the aluminum alloy“ADC6”. Subsequently, the amount of hydrogen generated was measured inthe same manner as Working Example 1. Table 7 shows the results. Themaximum reaction temperature of the hydrogen generating materialincluding 1 wt % heat generating material was 80° C. during the test.

Working Example 14

A hydrogen generating material was produced in the same manner asWorking Example 13 except that the magnesium alloy powder having anaverage particle size of 50 μm (the proportion of particles with aparticle size of 60 μm or less: 82 wt %) was mixed with calcium oxide ata ratio as shown in Table 7. Subsequently, the amount of hydrogengenerated was measured in the same manner as Working Example 1. Table 7shows the results.

Working Example 15

Instead of the magnesium alloy “MC10”, the following magnesium alloysbased on the JIS were used: “MC12” (composition: Mg content: 92 wt %, Zrcontent: 0.8 wt %, form: cutting chips); “MDC1B” (composition: Mgcontent: 90 wt %, Al content: 8.5 wt %, form: cutting chips); and “MC3”(composition: Mg content: 87 wt %, Al content: 9.5 wt %, Zn content: 2wt %, form: cutting chips). Three types of hydrogen generating materialswere produced in the same manner as Working Example 14 except that eachof the metal materials was mixed with calcium oxide at a ration as shownin Table 7. Subsequently, the amount of hydrogen generated was measuredin the same manner as Working Example 1. Table 7 shows the results.

TABLE 7 Metal material Average Content (wt %) Amount of Mate- particleMg Metal hydrogen rial size content mate- Calcium generated (JIS) (μm)(wt %) rial oxide (mL) Working MC10 10 94 99 1 210 Example 13 97 3 25195 5 247 90 10 264 85 15 201 80 20 168 70 30 130 Working MC10 50 94 95 5185 Example 14 85 15 198 80 20 96 70 30 87 Working MC12 50 92 95 5 183Example 15 MDC1B 90 191 MC3 87 190

In Working Examples 10 to 15, the surface treatment of the metalmaterial can be performed easily by using the aluminum alloy with highhardness or the magnesium alloy, and thus the amount of hydrogengenerated can be increased.

Working Example 16

Referring to FIG. 1, the pellets formed in Working Example 5 were placedin the vessel 2 of the hydrogen generator 1 as the hydrogen generatingmaterial 9. By using the tubular pump 6, water 10 flowed through thesupply pipe 7 and entered the vessel 2 from the inlet 4 so that thewater 10 was supplied continuously at a rate of 0.05 mL/min. Thus, thehydrogen generating material 9 and the water 10 reacted to producehydrogen. This hydrogen was drawn from the outlet 5 through thedischarge pipe 8 and supplied to the polymer electrolyte fuel cell 20 inFIG. 2. Then, the power generation of the fuel cell 20 was measured.Consequently, the fuel cell 20 yielded a high output of 200 mW/cm² atroom temperature, which ensures that the hydrogen functions sufficientlyas a fuel source for driving the fuel cell.

In this example, when the supply of water with the tubular pump 6stopped, the hydrogen generation stopped after several minutes.Therefore, the amount of hydrogen generated can be controlled bycontrolling the supply of water.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

As described above, the hydrogen generating material of the presentinvention can produce hydrogen easily and efficiently at lowtemperatures. A hydrogen generator can be made portable by using thehydrogen generating material of the present invention. Moreover, the useof the hydrogen generating material of the present invention as ahydrogen fuel source can reduce the size of a fuel cell and improve theelectrical efficiency.

1. A hydrogen generating material that reacts with water to producehydrogen comprising: at least one metal material selected from the groupconsisting of aluminum, magnesium, and their alloys; and a heatgenerating material that generates heat by reacting with water at roomtemperature, wherein the metal material includes particles with aparticle size of 60 μm or less in a proportion of 80 wt % or more, thehydrogen generating material comprises at least one oxide selected fromthe group consisting of an oxide of an alkali metal and an oxide of analkaline-earth metal as the heat generating material, and a proportionof the metal material to a total weight of the metal material and theheat generating material is more than 85 wt % and not more than 99 wt %.2. The hydrogen generating material according to claim 1, furthercomprising at least one compound selected from the group consisting ofcalcium chloride, magnesium chloride, and calcium sulfate as the heatgenerating material.
 3. The hydrogen generating material according toclaim 1, further comprising calcium oxide as the heat generatingmaterial.
 4. The hydrogen generating material according to claim 1,wherein the metal material is aluminum or an aluminum alloy.
 5. Thehydrogen generating material according to claim 1, wherein the metalmaterial is an aluminum alloy, and the aluminum alloy includes anelement other than aluminum in a proportion of 2 to 20 wt %.
 6. Thehydrogen generating material according to claim 1, wherein the metalmaterial is a magnesium alloy, and the magnesium alloy includes anelement other than magnesium in a proportion of 2 to 20 wt %.
 7. Thehydrogen generating material according to claim 5, wherein the aluminumalloy includes at least one element selected from the group consistingof silicon, iron, copper, manganese, magnesium, zinc, nickel, titanium,lead, tin, and chromium.
 8. The hydrogen generating material accordingto claim 6, wherein the magnesium alloy includes at least one elementselected from the group consisting of aluminum, zinc, zirconium,silicon, iron, copper, manganese, nickel, and a rare-earth element. 9.The hydrogen generating material according to claim 1, wherein the metalmaterial has a particle size of 0.1 μm or more.
 10. The hydrogengenerating material according to claim 1, wherein the metal material hasan average particle size of 30 μm or less.
 11. The hydrogen generatingmaterial according to claim 1, wherein the metal material is powderproduced by an atomizing method.
 12. The hydrogen generating materialaccording to claim 1, wherein the metal material is subjected to surfacetreatment that improves surface reactivity by a chemical or mechanicalmeans.
 13. The hydrogen generating material according to claim 12,wherein the surface treatment is performed by mechanically stirring themetal material in a solvent.
 14. The hydrogen generating materialaccording to claim 1, being in the form of pellets or granules.
 15. Thehydrogen generating material according to claim 1, wherein the metalmaterial is in the form of a scale.
 16. A hydrogen generator forgenerating hydrogen using a hydrogen generating material that reactswith water to produce hydrogen, comprising: a vessel having at least anoutlet through which hydrogen is discharged, wherein the hydrogengenerating material according to claim 1 is placed in the vessel. 17.The hydrogen generator according to claim 16, wherein the vessel has aninlet through which water is supplied.
 18. The hydrogen generatoraccording to claim 16, wherein the vessel has a storage portion forstoring water inside.
 19. A fuel cell comprising: a membrane electrodeassembly that comprises a positive electrode for reducing oxygen, anegative electrode for oxidizing hydrogen, and a solid electrolytelocated between the positive electrode and the negative electrode; andthe hydrogen generator according to claim 16, wherein hydrogen producedby the hydrogen generator is used as a fuel source.
 20. A method forproducing hydrogen comprising: supplying water to the hydrogengenerating material according to claim 1; and producing hydrogen by areaction of the water and the metal material included in the hydrogengenerating material.
 21. A hydrogen generating material that reacts withwater to produce hydrogen comprising: at least one metal materialselected from the group consisting of aluminum, magnesium, and theiralloys; and a heat generating material that generates heat by reactingwith water at room temperature, wherein a particle size of the metalmaterial is 100 μm or less, the hydrogen generating material comprisesat least one oxide selected from the group consisting of an oxide of analkali metal and an oxide of an alkaline-earth metal as the heatgenerating material, and a proportion of the heat generating material tothe whole hydrogen generating material is 1 wt % to 20 wt %.